Exocytotic fusion pores exhibit semi-stable states

Michael J. Curran, Fredric S. Cohen, Douglas E. Chandler, Peter J. Munson, Joshua Zimmerberg

Research output: Contribution to journalArticlepeer-review

66 Scopus citations


Rapid-freezing/freeze-fracture electron microscopy and whole-cell capacitance techniques were used to study degranulation in peritoneal mast cells of the rat and the mutant beige mouse. These studies allowed us to create a time-resolved picture for fusion pore formation. After stimulation, a dimple in the plasma membrane formed a small contact area with the secretory granule membrane. Within this zone of apposition no ordered proteinaceous specializations were seen. Electrophysiological technique measured a small fusion pore which widened rapidly to 1 nS. Thereafter, the fusion pore remained at semi-stable conductances between 1 and 20 nS for a wide range of times, between 10 and 15,000 msec. These conductances correspond to pore diameters 25-36 nm. Ultrastructural data confirmed small pores of hourglass morphology, composed of biological membrane coplanar with both the plasma and granular membranes. Later, the fusion pore rapidly increased in conductance, consistent with the observed morphology of omega-figures. The hallmarks of channel-like behavior, instantaneous jumps in pore conductance between defined levels, and sharp peaks in histograms of conductance dwell-time, were not seen. Since the morphology of small pores shows contiguous fracture planes, the electrical data represent pores that contain lipid. These combined morphological and electrophysiological data are consistent with a lipid/protein complex mediating both the initial and later stages of membrane fusion.

Original languageEnglish (US)
Pages (from-to)61-75
Number of pages15
JournalThe Journal of Membrane Biology
Issue number1
StatePublished - Apr 1993


  • electrophysiology
  • exocytosis
  • freeze-fracture
  • mast cells
  • membranes
  • secretion

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology


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